We present a rigorous investigation on elution behaviors of ultrasonically shortened multiwalled
carbon nanotubes in size-exclusion chromatography. The size separation of five
carbon nanotube samples that underwent ultrasonic shortening for varying lengths of time
revealed the existence of three kinds of carbon species: large nanotubes, small nanotubes,
and amorphous carbon species. Separation of the three different carbon species was confirmed
by SEM analyses on the fractionated eluates and also by light scattering/UV absorbance
double detection. The chromatographic peak intensity ratio between the large and
small nanotubes suggested an increased amount of small carbon nanotubes upon longer
mechanical treatment time. The effect of the concentration of carbon nanotube dispersion
on elution behavior was examined, and the elution volume of the shortened nanotubes was
found to decrease upon dilution while that of the large nanotubes showed the opposite tendency.
Unusual elution behaviors of the multiwalled carbon nanotubes were also observed
by altering the flow rate, and these behaviors could be explained by the longer equilibration
time taken for large nanotubes to access the pores of the packing materials and a possible
morphology change of small carbon nanotubes.